This invention relates to vibratory gyroscopes, and more particularly to silicon micromachined vibratory gyroscopes.
Multi-axis sensors are highly desirable for inertial sensing of motion in three dimensions. Previously, such sensors were constructed of relatively large and expensive electromagnetic and optical devices. More recently, micromechanical sensors have been fabricated using, semiconductor processing techniques. Microelectrical mechanical or xe2x80x9cMEMSxe2x80x9d systems allow formation of physical features using semiconductor materials and processing techniques. These techniques enable the physical features to have relatively small sizes and be more precise. Specifically, micromechanical accelerometers and gyroscopes have been formed from silicon wafers by using photolithographic and etching techniques. Such microfabricated sensors hold the promise of large scale production and therefore low cost.
In a vibratory gyroscope, the Coriolis effect induces energy transfer from the driver input vibratory mode to another mode which is sensed or output during rotation of the gyroscope. Silicon micromachined vibratory gyroscopes are integratable with silicon electronics. These devices are low cost, capable of achieving high Q factors, can withstand high g shocks due to their small masses, are insensitive to linear vibration and consume little power.
As the cost of manufacturing the vibratory gyroscopes decreases, other costs such as the cost of calibration of the gyroscope become a more significant portion of the total cost. Prior calibration using inertial testing required the use of a precision rotation table to perform various tumble and rotation maneuvers. What is desired is a system that calibrates a vibratory gyroscope at a significantly reduced cost.
The present invention enables the simulation of the Coriolis forces with electrostatic elements already present in the vibratory gyroscope. For vibratory gyroscopes, the Coriolis force may be at the same frequency as the vibrational frequency of the gyroscope, which may be small in magnitude. An artificial electrostatic rotation signal is added to the closed-loop force rebalance system. Because the Coriolis force is at the same frequency as the artificial electrostatic force, the simulated force may be introduced into the system to perform an inertial test on MEMS vibratory gyroscopes without the use of a rotation table. Magnetic force, piezoelectric actuators or any other actuator used for vibratory gyroscopes may be used to introduce a simulated Coriolis force into the sensor.